Unusually high prevalence rates for cataract, a common disease of essentially unknown etiology, have been reported for northwest India. This study is an epidemiologic survey of three geographically defined areas in Punjab, India, to gain insight into environmental, nutritional, and other risk factors for senile cataract. Special emphasis is directed to elements such as fluoride present in drinking water. An interview and ophthalmologic examination will be done for all subjects age 30 and over (about 4,500).